Rechargeable batteries are widely used in many products, such as laptop computers, tablets, mobile phones, and even large electric vehicles and robots. Since durability of those products depends on the performance of the rechargeable batteries, use of suitable rechargeable batteries and careful maintenance for them are very important during the lifespan of those products.
Recently, among all rechargeable batteries, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries and lithium batteries are more and more popular because they have stable physical characteristics and smaller size for stacking. They can also be charged or discharged with no or limited memory effects. Besides, these rechargeable batteries have very low self-discharge rate and high energy density. However, since they often use with sub-battery sets (or cells) connected in series/parallel, poor performance may be caused by unbalance of the sub-battery sets during charge or discharge. In order to avoid battery unbalance and utilize the best performance of these rechargeable batteries, monitor of power capacity of these rechargeable batteries is very commonly executed in battery management systems (BMS). Full charge capacity (FCC) is an index of power capacity. The FCC of a rechargeable battery is set to be a certain value when the rechargeable battery is produced in a factory. However, it will gradually decrease as the rechargeable battery is repeatedly charged and discharged. Thus, the FCC needs to be updated often for each rechargeable battery to check current status.
A prior art to determine the FCC of a rechargeable battery is disclosed in US Patent Application No. 20130057290. Please refer to FIG. 1. It is a flowchart of the mentioned application. A battery performs charging and discharging operations according to the control of a battery protection circuit (S1). When a charger is electrically connected to a battery pack, the charging operation is performed. When an electronic device is connected to the battery pack, the discharging operation is performed. A monitoring unit monitors each cell of the battery in series during the charging and discharging operations of the battery to measure at least one of voltage, current, and temperature of the battery (S2). A control unit receives monitoring results from the monitoring unit, and determines whether the monitoring results satisfy FCC updating conditions of the battery (S3). For example, the control unit determines whether the measured values of the voltage, the current, and the temperature of the battery matches the corresponding values stored in a preset table. If it is determined that the updating conditions are not satisfied in operation (S3), the process returns to operation (S1). In addition, the battery repeatedly performs the charging and discharging operations, and the monitoring unit performs the monitoring substantially continuously. On the other hand, if it is determined that the updating conditions are satisfied in operation (S3), it is determined whether the time point where the conditions are satisfied is included during a rising period of the voltage of the battery (S4). For example, it is determined whether the discharging operation of the battery is discontinued. When it is determined that the voltage of the battery rises in operation (S4), the process returns to operation (S1). On the other hand, when it is determined that the voltage of the battery does not rise, the FCC of the battery is updated and the updated FCC is stored in a recording unit (S5).
Although the prior doesn't point out a specified means to calculate the FCC, it indicates updating conditions that a calculated FCC for each cell in the battery is acceptable under the conditions. Meanwhile, since there are many rechargeable battery cells assembled inside the battery in series, the FCC of the battery is set to be the smallest FCC among the FCCs of the all rechargeable battery cells. As there will be slightly battery unbalance among the rechargeable battery cells during measurement, the FCC should reflect a real situation so that people know if the battery needs to repair or not. Once after repairing, some rechargeable battery cells are replaced, the updating conditions need to re-check again. It is too complex while operating.
Hence, a more simplified and effective method to search for FCC of stacked rechargeable battery cells during operation is desired.